The present invention relates to a device included in a distance meter system for transmitting audible information from an electronic distance meter to an operator placed at a reflector, such as a cube corner prism, towards which a distance measurement is to be made. The electronic distance meter is of the kind which has a transmitter, which emits a continuous measuring signal towards the reflector. The signal is in the form of an electromagnetic radiation, onto which a periodic signal is modulated. The distance meter includes a receiver, which receives the modulated radiation reflected by the reflector.
Electronic distance meters of phase comparison type measure the distance to a target by comparing the phase between the modulated signals on a transmitted, modulated light beam and on the light beam, which is received after reflection from the target. The light beam is modulated with a high frequency periodic signal, which most often is sinusoidal or a square wave signal. Common frequences for this modulating signal are ca 15 MHz and 150 kHz or 30 MHz and 300 kHz. Most distance meters of this type make measurements towards a reflector placed on the target, such as a cube corner prism or the like.
Gauging for staking out land, such as boundaries or the like, by the aid of an electronic distance meter (EDM) is usually made by placing a distance measuring instrument provided with the electronic distance meter on the land. A first measurement operation is made towards reference points having known positions. From the result of these measurements the exact position of the distance measuring device is calculated. Thereafter the acutal staking out is made. An operator stands by the distance measuring instrument and commands an operator, who carries a rod provided with a prism, to place the rod with the prism at a predetermined spot, determined by the boundaries of the land. The distance between the instrument and the spot, where the prism shall be placed, are sometimes long. The communication from the instrument operator to the prism operator is usually made by the aid of so called Walkie Talkies.RTM..
A Walkie Talkie.RTM. is principally a system of a radio transmitter and a radio receiver. The communication is transmitted as information modulated on a carrier. In cities and other densely populated regions use of such instrumentation is often problematic to, since congestion is very high at those frequencies which are allowed to be used. In some countries transmitter/receiver units of this kind are not even allowed. If Walkie Talkies.RTM. are used for communication from one operator to another working with a distance measuring equipment this also means that the operators outside the equipment must have separate units, which have to be handled in addition to other equipment necessary for the measurement.